Although memories may be stored in a variety of ways, increasing evidence suggests that at least some memories are stored as changes in the strength of connections between neurons. Recently two types of memory that involve changes in synapse strength or number, long-term potentiation (LTP) and cerebellar motor learning, have been associate with an increase in mRNA for tissue-type plasminogen activator (tPA). This suggest that tPA activity may facilitate motor learning. However, such a role for tPA has not been confirmed. Therefore, our first experiments test whether blocking tPA activity or deleting the tPA gene impairs cerebellar motor learning. In addition, we will determine whether tPA facilitates motor learning through the conversion of plasminogen to plasmin, and also whether motor learning in tPA-/- mice involves persistent modulations of GABAergic activity. Finally, the biochemical and molecular events that regulate tPA activity have not been identified. However, many examples of activity-dependent plasticity require activation of NMDA receptors and at least some of these are also associated with an increase in tPA mRNA. This suggest that NMDA receptors are involved in the regulation of tPA activity. Our final experiments will utilize pharmacological blockade of NMDA receptors to determine whether cerebellar motor learning requires activation of NMDA receptors and whether blocking those receptors during motor learning prevents the increase in tPA mRNA expression. Taken together these experiments will provide insight into tPA's role in memory formation and, more generally, into the mechanisms of activity-dependent plasticity.